The present embodiments relate to wireless communication systems and, more particularly, to the transmission of Physical Downlink Shared Channel (PDSCH) data and Physical Uplink Shared CHannel (PUSCH) data in multi-input multi-output (MIMO) transmissions.
With Orthogonal Frequency Division Multiplexing (OFDM), multiple symbols are transmitted on multiple carriers that are spaced apart to provide orthogonality. An OFDM modulator typically takes data symbols into a serial-to-parallel converter, and the output of the serial-to-parallel converter is considered as frequency domain data symbols. The frequency domain tones at either edge of the band may be set to zero and are called guard tones. These guard tones allow the OFDM signal to fit into an appropriate spectral mask. Some of the frequency domain tones are set to values which will be known at the receiver. Among these are Cell-specific Channel State Information Reference Signals (CSI-RS) and Dedicated or Demodulating Reference Signals (DMRS) in downlink, and user-specific Sounding Reference Signal (SRS) in uplink. These reference signals are useful for channel estimation at the receiver.